1. Field of the Invention
The present invention broadly relates to a variable-cylindered internal combustion engine such as a direct-type engine which is capable of varying the number of operative cylinders and, more particularly, to a cylinder control device which controls the operation of cylinders in such a variable-cylindered internal combustion engine.
2. Description of the Prior Art
FIGS. 12 and 13 in combination show a known movable-plunger type cylinder control device for a variable-cylindered engine, in different states of operation. In these Figures, a reference numeral 31 denotes a body, while a reference numeral 32 devotes a plunger which is slidably received in a bore 31a formed in the body 31. The body 31 is slidably disposed in a bore 36a of a block 36 which in turn is interposed between a cam 34 adapted to be rotated by the crackshaft of an engine and a valve stem 40 of valve 35
A reference numeral 37 designates a solenoid valve which is disposed in the oil passage 38, while a numeral 39 denotes a groove formed in the outer periphery of the body 31. A numeral 40 denotes a valve stem. A numeral 41 designates a spring which is loaded between the body 31 and the plunger 32 so as to bias the plunger 32 from the bore 31a in the body 31 of the plunger 32. A numeral 42 designates a snap ring which prevents the plunger 32 from coming off the bore 31a. A numeral 33 designates a computer which controls the solenoid valve 37 so as to selectively put the cylinder of the engine into operation.
A spring 43 is loaded between the body 31 and a spring retainer 45 which is fixed to the valve stem 40 by means of a cotter 44, while a valve spring 46 is interposed between the retainer 45 and the bottom surface of the bore 36a in the block 36. A reference numeral 47 denotes a valve guide, while a numeral 48 designates a groove which is adapted to engage with the upper end of the valve stem 40 during normal operation of the cylinder. A numeral 49 denotes an idle bore into which the upper end of the valve stem 40 escapes when the cylinder of the engine is inoperative, i.e., when the engine operate with reduced number of cylinders. The idle bore 49 is formed vertically in the central portion of the plunger 32.
In the state shown in FIG. 12, the lift of the cam 34 is transmitted through the body 31, plunger 32 and the valve stem 40 to the valve 35 so as to open and close the valve port thereby allowing the cylinder to operate.
When it is desired to reduce the number of the operating cylinders, as in the case of waiting at a crossing for a traffic light, the computer 33 delivers a signal to the solenoid valve 37 associated with the cylinder which is to be put into inoperative state. As a result, the solenoid valve 37 is opened, so that hydraulic pressure is transmitted through the oil passage 38 and the groove 39 to the plunger 32, thereby moving the plunger 32 against the force of the spring 41. As a result, the idle bore 49 is brought to a position just above the valve stem 40. In this state, even though the cam 34 is rotated to depress the body 31, the upper end of the valve stem 40 is received in the idle bore 49 in the plunger 32, so that the lift of the cam 34 is not transmitted to the valve 35. Thus, the valve port is kept closed, so that this cylinder is kept inoperative, as will be seen from FIG. 13.
This known cylinder control device, however, suffers from various problems.
A first problem resides in that the movement of the plunger 32 to the cylinder-inoperative position is impaired due to stagnation of oil in the portion of the plunger chamber 50 where the spring 41 is received, because there is no means for relieving oil from this portion of the plunger chamber 50.
Another problem resides in that, since the width of the groove 48 in the plunger 32 is too larger as compared with the diameter of the valve stem 40, the wall of the groove cannot serve as an effective means for preventing the rotation of the plunger 32 during assembly or operation due to, for example, vibration. Once the plunger is rotated, the idle bore 49 is circumferentially offset from the position of the valve stem, so that the cylinder cannot be turned into inoperative state.
A third problem resides in that, since the space between the retainer 45 fixed to the valve stem 40 and the body 31 is small, the return spring 43 for upwardly biasing the body 31 into contact with the cam 3 can have only a limited size and, hence, can exert only a limited upward biasing force. In addition, since the force for lifting the valve stem 40 for closing the valve is the difference between the force of the valve spring 46 and the return spring 43, only a small force is available for lifting the valve stem to close the valve. This means that the valve cannot follow the cam during high speed engine operation.
A fourth problem resides in that the plunger 32 has to have a large diameter in order that the idle bore 49 formed therein has a size large enough to receive the upper end portion of the valve stem 40 when the cylinder is in inoperative state. In consequence, the size of the cylinder control device as a whole is increased undesirably. In addition, the large diameter of the plunger requires a large quantity of oil for displacing the plunger.
A fifth problem resides in that, since the bottom surface of the groove 48 in the plunger 32 is flat, the valve clearance is undesirably changed by a slight rotation of the plunger 32 with respect to the valve stem 40, thus impairing smooth operation of the engine.